1. Field of the Invention
The present invention is related to an extracorporeal lithotripsy apparatus, having an ultrasound generator for generating a pressure wave, which may be focused to disintegrate calculi in a patient.
2. Description of Prior Art
The disintegration of calculi by the use of a lithotripsy apparatus is achieved by emitting shock waves focused on calculi in vivo. The shock waves are focused by a determination of the focal range, within which the shock waves must be directed in order to disintegrate calculi in a patient. The focal range, necessary to focus a pressure wave capable of disintegrating the calculi, is determined by either an x-ray system, having an x-ray radiator and radiation receiver, or an ultrasound locating system. The ultrasound system is centrally located in the shock wave head, so that the central rays of the ultrasound system and the shock wave head coincide. An x-ray system may be used for initially locating the position of calculi, and an ultrasound system is preferred for determining subsequent changes in the locations of calculi during treatment. Under these circumstances it is preferable, to arrange the ultrasound locating system within the shock wave head so that it is removable, allowing the central region of the shock wave head to be further employed for the unattenuated transmission of x-rays.
A device which permits removal of the ultrasound locating system from the center of the shock wave head, while preventing the coupling fluid from running out, is disclosed in EP-A-0316863. A hollow-cylindrical air-filled space, which limits the space filled with coupling fluid, and does not attenuate x-rays, is provided for acceptance of the ultrasound system within the center of the shock wave head. This space is exposed (open) on the application side, and thus permits contamination of the space to occur.